Many fuel cells conventionally employ internal membranes. One example of such fuel cells are the so-called PEM type which have proton exchange membranes, also referred to as polymer electrolyte membranes. The membranes, in order to perform properly, must be kept moist and must not be subjected to inordinately high temperatures.
To provide proper operation of a fuel cell system, it is therefore necessary that means be provided so that the fuel cell membranes are wetted to the proper degree to avoid damage to or shorten the life of the membranes as well as to maintain a desired, high degree of efficiency of operation.
Moreover, in some fuel cell systems, reformers are required to convert a hydrogen-containing organic material to a hydrogen rich fuel stream for consumption within the fuel cell. Various hydrogen-containing organic compounds have been suggested for the purpose including methanol, ethanol, natural gas, conventional gasolines, diesel fuel, propane, butane, etc. In the case of certain of these materials, it is necessary to humidify the incoming gas stream prior to its admission to the reformer to achieve the desired conversion to a hydrogen rich fuel stream.
Further, in fuel cell systems, it is also highly desirable that the incoming fuel and oxidant streams be at a desired operating temperature of the fuel cell and be at a desired range of relative humidity to maximize membrane efficiency over a wide range of operating conditions of the fuel cell, particularly where loading of the fuel cell varies over a substantial range.
In the usual case, humidification and/or temperature control of the various streams that may require humidification is achieved by heating water or another aqueous water-based material to cause the same to evaporate within the stream and raise the relative humidity thereof. This, of course, requires the expenditure of energy to generate the heat of vaporization. As fuel cell efficiencies are desirably maximized, it is highly desirable that the energy expended in the fuel cell system for providing the desired heat for humidification purposes be minimized or at least obtained in a way such that the fuel requirements of the fuel cell system are minimized.
The present invention is directed to meeting the above needs.